The present invention relates to materials used suitably for forming a multicolor image by use of a laser beam and a method for forming the multicolor image by use of the materials.
In the field of graphic art, printing plates are printed by use of a set of color separation films prepared from a color original by use of lith films. In general, in order to check errors in the color separation process or necessity of the color correction before printing (practical printing operation), a color proof is prepared from color separation films. To the color proof, realization of high resolving power that enables high reproduction of medium images and performance such as high stability to the process are expected. Furthermore, in order to obtain the color proof similar to practical printed matter, materials practically used for printed matter are preferably used as materials for the color proof, for example, actual printing paper (regular paper used in running on to give a final product) is used as a base and pigments are used as coloring materials. Moreover, for the preparation of the color proof, a dry process where no developing solution is used has been highly desired.
With contribution of an electronic system in the latest pre-process of printing (prepress field), a recording system for preparing directly the color proof from digital signals has been developed as the dry process for preparing the color proof. This electronic system aims at preparing the color proof of a particularly high image quality. In general, a dot image of 150 lines/inch or more are reproduced. In order to record the proof of a high image quality from the digital signals, the laser beam that can be modulated by digital signs and can be stopped down as recording beams are used as recording heads. Recording materials having high recording sensitivity to the laser beam and high resolving power that enables reproduction of highly fine halftone dots must be developed.
Known recording materials used for a method for forming a transfer image by making use of the laser beam are hot melt transfer sheets having a light-to-heat conversion layer that absorbs the laser beam to generate heat and an image-forming layer that contains pigment dispersed in components such as a hot melt wax and a hot melt binder on a support in this order (Japanese Patent Laid-Open No. 58045/1993). In the method for forming images by using these recording materials, heat generated in areas irradiated with the laser beam in the light-to-heat conversion layer melts the image-forming layer corresponding to the areas, and the melted areas transfer to an image-receiving sheet laminated on a transfer sheet to form a transfer image on the image-receiving sheet.
Furthermore, Japanese Patent Laid-Open No. 219052/1994 discloses a thermal transfer sheet where a light-to-heat conversion layer containing a light-to-heat convertible substance, a heat peel layer formed of a very thin film (0.03 to 0.3 xcexcm), and an image-forming layer containing a coloring material are provided on a support in this order. In this thermal transfer sheet, binding power between the image-forming layer and the light-to-heat conversion layer that are bound through the aforesaid heat peel layer reduces by irradiation with the laser beam to form a highly fine image on an image-receiving sheet laminated on the thermal transfer sheet. In this method for forming images by use of the thermal transfer sheet, the so-called xe2x80x9cabrasionxe2x80x9d is utilized. This phenomenon is utilized as follows: In areas irradiated with a laser beam, the heat peel layer is partly decomposed and vaporized, the binding power between the image-forming layer and the light-to-heat conversion layer in the areas is weakened, and the image-forming layer in the areas is transferred to the image-receiving sheet laminated thereon.
These methods for forming images have the advantages in that the actual printing paper having an image-receiving layer (adhesive layer) attached can be used and the multicolor image is obtained with ease by transferring successively images different in color to the image-receiving sheet. These methods enable easy formation of highly fine images and are useful for the preparation of the color proof (DDCP: direct digital color proof) or a highly fine mask image.
In the materials used for the methods for forming the multicolor image, the light-to-heat conversion layer and the image-forming layer of the thermal transfer sheet are formed by a coating method. In addition, the image-receiving layer on the image-receiving sheet also is formed by the coating method. Furthermore, the image-forming layer of the thermal transfer sheet requires a uniformly coated surface in order to acquire stable transfer (sensitivity). Non-uniformly coated surfaces produce irregularities in evenness of the surfaces, surface energy, and adhesive powder, resulting in deteriorating uniform transfer to the image-receiving sheet. Moreover, the image-receiving layer of the image-receiving sheet also requires uniformly coated surface for stable transfer of an image formed on the image-forming layer of the thermal transfer sheet without irregularities in transfer.
Accordingly, an aim of the invention to provide materials used appropriately for the method for forming the multicolor image and having anyone sheet or both sheets of a thermal transfer sheet which has an image-forming layer with a uniformly coated surface and is improved in properties of transferring of an image formed on the image-forming layer to an image-receiving sheet and an image-receiving sheet which has an image-receiving layer with a uniformly coated surface and is improved in the properties of transferring of the image formed on the image-forming layer from the thermal transfer sheet.
Another aim of the invention is to provide a method for forming the multicolor image by use of the materials having acquired excellent performance by the improvement in the properties of transferring.
In order to achieve the aims, the invention provides materials for forming the multicolor image that have the following constitution and a method for forming the multicolor image by use of the materials.
1. Materials for forming a multicolor image where by use of an image-receiving sheet having at least an image-receiving layer on a support and four kinds of thermal transfer sheets different in color and each having at least a light-to-heat conversion layer and an image-forming layer on a support, images are recorded by superposing the respective thermal transfer sheets and the image-receiving sheet so that the image-forming layer of the respective thermal transfer sheets and the image-receiving layer of the image-receiving sheet face each other, irradiating with a laser beam, and transferring the image-forming layer""s areas irradiated with the laser beam to the image-receiving layer of the image-receiving sheet wherein at least one of layers contained in the image-receiving sheet and/or the respective thermal transfer sheets contains a fluorine-series surface active agent of a homopolymer prepared from a polymerizable monomer represented by the following formula (1) and having a weight average molecular weight Mw of 3000 or more:
CnF2n+1xe2x80x94Lxe2x80x94CH2CH2xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CRxe2x95x90CH2xe2x80x83xe2x80x83(1)
(In formula (1), n represents an integer of from two to 14. R represents a hydrogen atom or an alkyl group having one to 10 carbon atoms. L represents a single bond or a divalent organic group containing at least one atom selected from an oxygen atom, a nitrogen atom, a sulfur atom, and a carbon atom.)
2. The materials as described in the preceding item 1 wherein the fluorine-series surface active agent is contained in the image-forming layer of the respective thermal transfer sheets.
3. The materials as described in the preceding item 1 wherein the fluorine-series surface active agent is contained in the image-receiving layer and/or a cushion layer of the image-receiving sheet.
4. The materials as described in the preceding item 1 wherein the fluorine-series surface active agent is contained in the image-forming layer of the respective thermal transfer sheets and the image-receiving layer and/or the cushion layer of the image-receiving sheet.
5. The materials as described in the preceding items 1 to 4 wherein the fluorine-series surface active agent comprises a homopolymer prepared from a polymerizable monomer represented by the following formula (2):
CnF2n+1xe2x80x94CH2CH2SO2N(xe2x80x94R1)xe2x80x94CH2CH2xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CRxe2x95x90CH2xe2x80x83xe2x80x83(2)
(In formula (2), R1 has the same meaning as R in formula (1) and n is the same as n in formula (1).)
6. A method for forming a multicolor image through a process for image recording where by use of an image-receiving sheet having at least an image-receiving layer on a support and at least four kinds of thermal transfer sheets for yellow, magenta, cyan, and black each having at least a light-to-heat conversion layer and an image-forming layer on a support, the respective thermal transfer sheets and the image-receiving sheet superposed so that the image-forming layer of the respective thermal transfer sheets and the image-receiving later of the image-receiving sheet face each other are irradiated with a laser beam to transfer the image-forming layer""s areas irradiated with the laser beam to the image-receiving layer of the image-receiving sheet wherein the thermal transfer sheets and the image-receiving sheet of the materials for forming the multicolor image as described in any one of the preceding 1 to 5 are used as the thermal transfer sheets and the image-receiving sheet as described above.